Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$106.41	3.289%	$109.9098	$109.91	$109.90	$109.90
Purchase #2	$18.98	10.220%	$20.9198	$20.92	$20.90	$20.90
Purchase #3	$13.55	8.717%	$14.7312	$14.73	$14.75	$14.70
Purchase #4	$87.46	4.701%	$91.5715	$91.57	$91.55	$91.60
Purchase #5	$171.91	4.466%	$179.5875	$179.59	$179.60	$179.60
Purchase #6	$12.44	4.663%	$13.0201	$13.02	$13.00	$13.00
Purchase #7	$219.96	7.208%	$235.8147	$235.81	$235.80	$235.80
7 purchase totals =	$630.71		$665.5546	$665.55	$665.50	$665.50